Apparatus for irradiating objects with selected uniform doses of radiation



Feb. 17, 1970 Filed Oct. 21, 1965 w. w. KIRKPATRICK- ET AL UNIFORM DOSES0F RADIATION APPARATUS FOR IRRADIATING OBJECTS WITH SELECTED v 5Sheets-Sheet 1 Feb. 17, 191

Filed Oct. 21, 1935 W. W. KIRKPATRIC ETAL APPARATUS FOR IRRADIATING OBJC S WITH SELECTED UNIFORM DOSES OF RADIATION 5 Sheets-Sheet 3 Feb. 17,1970 w. w. KIRKPATRIC ETAL 3,496,362

APPARATUS FOR IRRADIATING OBJ C 5 WITH SELECTED UNIFORM DOSES OFRADIATION Filed 001;. 21, 1965 I 5 Sheets-Sheet 4 1970 w. w.KIRKIPATQRICK ET L 3,496,362 APPARATUS FOR IRRADIATING OBJECTS WITHSELECTED UNIFORM DOSES OF RADIATION Filed 0st. 21, 1965 5 Sheets-$heet 5FIG. 5

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United States Patent 3,496,362 APPARATUS FOR IRRADIATING OBJECTS WITHSELECTED UNIFORM DOSES OF RADIATION William W. Kirkpatrick, Ottawa,Ontario, and John Masefield, Montreal, Quebec, Canada, assignors toAtomic Energy of Canada Limited, Ottawa, Ontario, Canada, a corporationFiled Oct. 21, 1965, Ser. No. 505,223 Int. Cl. G21h /00 US. Cl. 250106 4Claim ABSTRACT OF THE DISCLOSURE Apparatus for selecting and applyingvarying dose rates of radiation to an object is described. The apparatusincludes means for shielding radioactive sources while a sample is beingmoved into and out of a radiation zone within the apparatus, and meansare provided for selecting and moving varying numbers of the radioactivesources into radiating positions around the sample. Fluid pressure isused for moving the radioactive sources into radiating positions, and aplurality of the radioactive sources may be moved at one time by asingle source of fluid pressure.

This invention relates to an apparatus for subjecting a sample to afield of influence and particularly, but not exclusively, to anapparatus for irradiating a sample with radioactive energy from aradioactive source.

Previously-known techniques of irradiation required that a sample beplaced in a large room in the vicinty of a radioactive source. This wasa disadvantage as the samples had to be taken into the room by theoperator and because of this, special clothing had to be worn by theoperator when entering the irradiating room. Furthermore, theconstruction of a special shielded room for irradiating samples wascomparatively expensive and space-consuming.

To change the dose rate of radioactive energy, i.e. to change theintensity of the field of influence, when a special room was provided itwas normally necessary for the operator to re-enter the room and changeor modify the radioactive source, i.e. the source of the field ofinfluence. This is, of course, a disadvantage.

It is also known in the prior art to provide for apparatus wherein asample can be placed within a radiation zone within the apparatus, andvarious arrangements have been attempted and provided for moving asource of radiation into position for irradiating whatever sample is tobe treated. However, such prior art devices have not provided forcomplete versatility in selecting and varying precise radiation doserates while, at the same time, providing for a uniform irradiation ofthe sample or object being treated.

The present invention provides for apparatus which can be easilyoperated to select and apply varying, but uniform, irradiation to asample or object. The apparatus includes a housing having a shieldedirradiating chamber, and means are provided for carrying andtransferring an object between a position exterior to the irradiatingchamber and a working position within the radiating chamber. A pluralityof guide tubes are positioned within the housing and around theirradiating chamber, and a radioactive source is carried in each guidetube so as to be movable from an isolated position to an irradiatingposition which is adjacent to an object placed in the irradiatingchamber, Each of the radioactive sources is individually operable in itsrespective guide tube by fluid-pressureoperated means associated withthe apparatus. The fluidpressure-operated means may include a series ofplenum channels through which fluid pressure is applied to one or moreof the guide tubes for moving one or more of the radioactive sourceswithin the guide tubes. In accordance with the invention, a specificnumber of radioactive sources may be selected and moved to irradiatingpositions to apply a known dose rate to the sample or object. Means areprovided for selecting and moving one, all, or combinations of theradioactive sources for adjusting dose rates, and whatever number isselected may be evenly spaced around the sample so that the selecteddose rate will be uniformly applied to the sample. Also, means may beprovided for rotating the sample or object relative to the radioactivesources.

One embodiment of the invention will now be described, by way ofexample, with reference to the accompanying drawings in which:

FIGURE 1 is a side view, partly in section, of apparatus for irradiatinga sample from a radioactive source;

FIGURE 2 is a view, partly in section, of the source cage assemblyutilized in the apparatus of FIGURE 1;

FIGURE 3 is a cross-sectional view of the apparatus shown in FIGURE 2taken along the line IIIIII to show the arrangement of the pencils;

FIGURE 4 is a perspective view of part of the apparatus shown in FIGURE1;

FIGURE 5 is a side view, partly in section, of the drawer top assemblyutilized in the apparatus of FIG- URE l, and

FIGURE 6 is a front view of the control panel used for controlling theapparatus of FIGURE 1.

In the different figures the same reference numeral has been applied tolike parts throughout.

In FIGURE 1, apparatus for irradiating a sample from a radioactivesource is illustrated together with its associated equipment mountedwithin a protective shroud assembly 1. A body of shielding material 2,contained therein, houses a source cage assembly 3 and an elongatedcylindrical drawer assembly 4, disposed along the longitudinal axis ofthe body of shielding material and within the source cage assembly. Thedrawer assembly 4 is made up of four basic sections; a lower extension5, a depleted uranium base 6, a sample chamber 7 and an upper extension8. The drawer assembly is capable of being raised and lowered by a cranearrangement 9 which is used to raise the drawer assembly 4 to a loadingposition, as indicated by the dotted lines in FIGURE 1, or to lowerirradiating position within the source cage assembly 3 as shown. Whenthe drawer assembly is in the upper loading position access to thesample chamber is effected by raising a Plexiglas protector 11 andremoving doors 14 which are provided on the sample chamber. As a safetyprecaution, when the drawer assembly is in its upper loading positionand the sample chamber doors -14 are removed, spring loaded plunger (notshown) hold the drawer up. Replacing the sample chamber doors allows thedrawer assembly to be lowered to the irradiating position. The samplechamber 7 is provided with a drain tube 12 which extends from the bottomof the sample chamber 7 to the outside of the body of shielding materialvia a drain pipe 13 protruding from the bottom of the source cageassembly. A head plug 10, having a cavity therein to provide themovement of the drawer assembly, seals the top of the body of hieldingmaterial and can be removed when access to the source cage assembly 3 isrequired.

Referring now to FIGURES 2, 3 and 4 illustrating the source cageassembly 3, it will be seen that a pencil guide tube assembly 17 isprovided comprising pencil guide tubes 29 disposed in a circle andlocated within a cavity provided by the body of shielding material 2(FIGURE 1). The inner diameter of the pencil guide tube assembly 17 ismade greater than the outer diameter of the drawer 3 assembly 4 topermit the latter to be slidably located within the pencil guide tubeassembly.

Thirty-six (or thirty-two as shown in the drawings) pencil guide tubes29 are disposed around the cavity and are equally spaced from eachother. These tubes may be of any convenient size and are arranged toform a pattern as shown in FIGURES 2 and 3. Each pencil guide tube 29includes therein an elongate radioactive pencil 18 which is a loose fitin the respective tube. A uranium plug 19 which is a close running fitwithin the tube is provided on the upper end of each pencil and acts asa piston. The uranium plug 19 is encased in 400 series stainless steelsleeves to prevent conflict of bearing metals and is capable ofoperating indicating switches as explained below.

In operation, the drawer assembly 4 is lowered into the source cageassembly 3 so that the sample chamber 7 assumes an irradiating position.The sample 20 is still isolated from radioactive energy due to theshielding effect of the depleted base 6, the lead shield blocks 21 andthe uranium plugs 19.

When irradiation is required, a selected number of pencils,corresponding to the dose rate required, are moved so as to be in theirupper position adjacent the sample chamber by introducing air underpressure into the respective tubes below each associated plug. In orderto facilitate removal of the source assembly and connection to the airsupply, air plenums 22 are wrapped around the pencil guide tube assembly17 in the form of a helix. Six plenums are provided so that each of sixgroups of pencils can be operated independently. In order to provideapparatus having maximum versatility, each pencil must be capable ofbeing put in any of the six groups. It is arranged that each pencilguide tube goes through each plenum once and any desired pencil may becontrolled by the pressure in a respective plenum by drilling an airentry hole, such as 23 in FIGURE 4, in the wall of the respective tubewhere it passes through the plenum. Air pressure to the six plenums isprovided by a pneumatic system 15 (FIGURE 1), via pipe 16 (FIGURE 1),connected to a plenum entry hole 24 (FIGURE 2). The apparatus includesseven pipes 16, six being used for the supply of air and the seventhbeing used for exhaust. O- ring seals are used for the pipe connections.

On pressurizing a plenum, all the pencils contained in those tubesassociated with the pressurized plenum are blown up to the irradiateposition. Air passing around the plug 19 passes into the upper housing25 of the source cage assembly and through an exhaust 26. When in theirradiate position the presence of the pencil is indicated by therelease of a reed contact 27 which is normally held closed by an Alnicomagnet 28 on the opposite side of the running tube. The magnet and reedcontact are disposed substantially parallel to each other and each ispositioned on its respective side of the tube assembly. When the pencilsare in the irradiate position the plug sheath, which is made of 400series stainless steel, acts as a magnetic short circuit and therebyreleases the contact.

If only a small number of pencils, for example one, is used to give alow dose rate normally the distribution of the radiation around thesample would be uneven. To overcome this disadvantage, means forrotating the complete drawer assembly at approximately 30 rpm. isprovided by the attachment shown in FIGURES 1 and 5. Rotation of thedrawer assembly, and therefore the sample in the sample chamber, isaccomplished after lowering the drawer assembly so that the upper partof the drawer assembly rests on a belt-driven rotating sheave 31 whichis of a larger diameter than the drawer assembly as shown in FIGURE 5.The belt is driven by a motor sheave 30 (FIGURE 1). A friction disk 32on the upper flange 33 causes the rotation of the sheave to betransmitted to the drawer assembly. The lifting ring 34, the lift plate35, and the drawer upper-plate 36 float free when the load is removedfrom the lifting ring.

A control panel, as shown in FIGURE 6, is provided to operate theirradiating apparatus. The time-exposure controls are mounted on thecontrol panel together with switches and indicating lamps. A key switch40 is provided to connect the power for operating the equipment and afuse 41 and an indicator lamp 42 are connected in the same circuit asthe key switch 40. The period of irradiation can be selected bypre-setting the counter 43 and depressing the appropriate switch onselector switch 44. The selector switch 44 has four positionsmanual,seconds, minutes, and hours. By depressing one of these the counter unitbecomes associated with those units of time as indicated by thedepressed switch. To select the proper dose rate six switches 45 areprovided each associated with a separate indicator lamp 46. The switches45 control the pneumatic system which provides the air pressure to theplenums for moving the radioactive pencils. Each switch is associatedwith a diflerent plenum and any number of switches can be depressed atthe same time. The drawer assembly is raised and lowered by the up-downswitch 48 and may be rotated by depressing the drawer assembly rotationswitch 47.

The operation of the apparatus in use will now be described in detail.With the drawer assembly in the loading position a sample to beirradiated is first inserted into the sample chamber. The sample chamberdoors are then put into closed position and the drawer assembly islowered into the body of shielding material. With the drawer assembly inthe lowered position the sample is located at the irradiating positionand substantially isolated from the radioactive source. The timeexposure for the chosen dose rate of radioactive energy is selected bymeans of a counter associated with a timing unit switch and theradioactive pencils to be blown up are selected by means of switches.The selected plenums are pressurized and all the pencils associated withsaid pressurized plenums are thus blown upwards to the irradiateposition. To obtain a suflicient selection of dose rate each plenum isconnected to a differently numbered pencil guide tube so that adiiferent number of pencils are forced upwards for each plenum chamber.Such an arrangement permits one, or all, or any combination of pencilsto be moved to the irradiate position. To determine if the correctnumber of pencils is at the irradiate position corresponding to thepressing of the associated switch, a plurality of indicator lights, onefor each switch, are provided to indicate that all the pencilsassociated with the respective plenum have moved to the irradiatepositon, When small dose rates are used, in the drawer assembly may berotated, by depressing the drawer assembly rotation switch, to provide auniform distribution of radioactive energy on all surfaces of thesample. When the exposure time has expired, the plenums areautomatically depressurized and those radioactive pencils in theirradiate position drop to their storage position. The drawer assemblyis raised to the loading position and the sample, having been subjectedto the desired radiation, is removed from the sample chamber. The nextsample can then be inserted in the sample chamber and the operationrepeated.

It will be appreciated that the number of guide tubes and radioactivepencils used is not restricted to 36 (or 32) but may be any convenientnumber.

By using the embodiment described it will be seen that a sample can beirradiated with radioactive energy and the dose rate selected withlittle risk to the operator. Furthermore, the apparatus, as described,is self-contained and does not require a separate, specially-protectedroom to be provided. However, it will be appreciated that the inventionis not restricted thereto.

We claim:

1. Apparatus for irradiating a sample with radiation from a radioactivesource, said apparatus including a housing of shielding materialdefining an irradiating chamber,

a drawer assembly for carrying a sample to be irradi- 3. Apparatusaccording to clam 1 including means for ated, rotating the samplerelative to the radioactive sources and transfer means for moving saiddrawer assembly beabout an axis parallel to the longtudinal axes of theguide tween (a) a loading position exterior to the chamber tubes whenthe sample is in the working position. at which a sample can be safelyloaded into the 4. Apparatus according to claim 1 and including meansdrawer assembly and (b) a working position within 5 for moving saidradioactive sources from working posithe chamber, tions to isolatedpositions within said housing by depresa plurality of guide tubes withinthe housing, said guide surizing individual guide tubes associated witheach of tubes being located in a cylindrical array around saidradioactive sources. the chamber, a radioactive source in each guidetube and movable 10 References Cited 3315 131333? 5335513? 52? oi iii igfilif-ifi UNITED STATES PATENTS n r 1 11 jacent said working position toirradiate a sample 2,866,905 12/1958 Yeomansin said drawer assembly atsaid working position, r 2,965,761 12/1960 Horvathand a series ofindividually operable fluid-pressure- 2368,7341 1/1961 Yeomans' operatedasemblies each including a plenum channel 3,088,032 4/1963 Bum-tomcommunicating with the interior of at least one of 3123713 3/1964 Maudat said guide tubes, with at least one of said plenum 3,132,251 5/1964Magnd et channels communicating with a plurality of guide 3,153,72510/1964 Ataxtubes, and each fluid-pressure-operated assembly 203,310,676 3/1967 Haram 250 "108 being operable to move respectivesources in respective guide tubes from isolated positions to workingRALPH NILSON Pnmary Exammer positions. S. ELBAUM, Assistant Examiner 2.Apparatus according to claim 1 wherein the plenum 25 channels are formedby channels extending around the U8. Cl. X.R.

guide tubes in a helical manner. 250-408 g; g UNITED STATES PATENTOFFICE CERTIFICATE OF CORRECTION Patent No. 3,496,362 Dated Eehm 11 J91Inventor(s) William w, Kirkpatrick and John Masefield It is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

The claim for priority in the heading of the above patent grant has beenomitted and should read as fellows:

--Claims priority 1iccizL-on Canada filed October lfle -f J, Cris- 1 N0.9l5,37i5--.

SIGNED AN!) $15, 11.58

Attest:

EdwardMFlewhaJr.

Attesting Officer wmm Commissioner of Patents

